An I-band calibration of the SBF method at blue colours(3)

An I-band calibration of the SBF method at blue colours

S.Mieskeetal.:SBFcalibrationatbluecolours3

tionsfromWorthey(1994)1andthosethat

use

the

alternatestel-

lar

evolutionary

isochrone

library

fromBertelliet

al.(1994)2

.Forthe

sakeofclarity,weseparatethemodelpredictionsintotwodi erentplots.

Forredcolours,allmodelstraceequation(1)reasonablywell,withtheoriginalWorthey-modelsandthoseofBlakesleeetal.beingmoredeviantfromtheempiricalcalibrationthantheothermodels.Inthebluerange,thereisanotablediscrepancybetweenthemodelpredictions:theoriginalWorthey(1994)modelsandthoseofLiuetal.(2000)predictacolourinde-pendent

MIcausedby

agedi erences.Thosemodelspredictacontinuationofequa-tion(1)forintermediateagesanda atteningoftherelationforveryoldages.At(V I)0 0.90thisleadstoanuncertaintyofupto0.5maginrelating

MI= 2.0+2.25×((V I)0 1.09)mag

(2)

ThiscaserepresentsthetheoreticalSBFmodelsplottedintheleftpanelofFig.1,whichviewedasawholesuggestanon-zerobutshallowerslopethanthatoftheempiricalcalibrationatreddercolours.SeecaseC)belowforthereasonofchoosing(V I)=1.09ascolourlimit.

CaseC:Thisisequation(1)appliedfor(V I)0>1.09andaconstantof

MI 2.0mag

ofthemodelsintherightpanelofFig.1matchesthevalueof

MI= 2.00mag,likeincase

C).Thisisappliedtoallgalaxieswith(V I)0<1.09whosedistanceincaseB)islargerthanthemeandistance.Inotherwords,galaxieswith

MI= 2.00mag,whilethosebelowareassigned

relation(1).ThemeandistanceobtainedwiththiscaseisofcourseveryclosetothatincaseB).

aa

CarnegieObservatoriesSystemforMultiObjectSpectroscopy,http://llama.lco.cl/aoemler/COSMOS.html

3